Semiconductor Devices and Applications

Diffusion of electrons and holes causes the depletion region.

A P-N junction mimics a closed switch when it has a low junction resistance.

 It is incorrect.

Ratio of e/m of an electron = 1.759 x 10 ¹¹ C/kg.

Statement (a) is correct: It increases the potential barrier. Statement (b) is wrong: It increases the space charge width and statement (c) is wrong: It increases the magnitude of electric field.

Statement (a) is true. Silicon is the most common material used to build semiconductor devices.Statement (b) is false. Si is the main ingredient of Sand. Statement (c) is false. Atoms in a pure silicon wafer contains four electrons in outer orbit (called valence electrons).

Statement (a) is true.  Diode converts ac input voltage to a pulsed dc output voltageStatement (b) is true: Diode introduces a 0.6V drop so o/p peak is 0.6V smaller than the i/p peak.Statement (c) is false: The o/p frequency is same as the i/p frequency.

Statement (a) is wrong. Photodiode is a 2 lead semiconductor device that transforms light energy to electric current. Statement (b) is correct. Photodiodes have very linear light v/s current characteristics.
Statement (c) is wrong. Photodiodes are more sensitive than photo-resistor.

Statement (a) is true. Junction field effect transistors like BJTs are three lead semiconductor devices. Statement (b) is false. JFETs are normally ON when VG - VS = 0. Statement (c) is true. Unlike BJTs, JFETs do not require a bias current and are controlled by using only a voltage.

Statement (a) is wrong. Special semiconductor crystal, such as cadmium sulfide or lead sulfide is used to make photo-resistors. Statement (b) is also wrong. When this semiconductor is placed in dark, electrons within its structure resist flow through the resistor because they are too strongly bound to the crystal’s atoms. Statement (c) is also wrong. Liberated electrons contribute to the current flowing through the device.

Statement (a) is false: An AC to DC power supply is built using a transformer and a full-wave rectifier. Statement (b) is true: Transformer is used to step down the voltage i/p. Statement(c) is true: Rectifier converts AC to pulsed DC.

Statement (a) is true. Solar cells are photodiodes with very large surface areas.Statement (b) is true. Solar cells yield more power. Statement (c) is true. A single solar cell may provide up to 0.5V that can supply 0.1A when exposed to bright light.

Statement (a) is true. Phototransistor is a light sensitive transistor.Statement (b) is false. When the light sensitive surface at the base is kept in darkness, the collector-emitter pair of the BJT does not conduct.Statement (c) is false. When the light sensitive surface at the base is exposed to light, a small amount of current flows from the base to the emitter. The small base-emitter current controls the larger collector-emitter current.

Statement (a) is false. A phototransistor is being used as a frequency counter or tachometer. Statement (b) is false. A rotating disk is connected to a rotating shaft. The rotating disk has one hole in it. Statement (c) is true. A frequency counter is used to count the number of electrical pulses generated.

Statement (a) is false. Used for displaying numbers and other characters. Statement (b) is false. 7 individual LEDs are used to make up the display. Statement (c) is false. When a voltage is applied across one of the LEDs, a portion of the 8 lights up.